This invention relates to plant growing media, and to a process for converting composted organic materials produced by optimised composting procedures into plant growing media for agronomic and other uses.
The successful production of crops in greenhouses requires an adequate and consistent quality of growing media for the crops. This can range from natural soils to soilless hydroponics. The key characteristics of growing media include consistent bulk density, ease of use, freedom from plant diseases and pests, and the ability to supply plant nutrients and water.
A high proportion of the potting soils and the like currently commercially available utilize peat, derived from harvesting natural peat bogs. For example Kim in U.S. Pat. No. 5,662,724 describes an artificial soil composition in which the major ingredients are in percentages by weight 10-30% peat, 10-30% granular soil, 40-60% sewage sediment, and 24-45% sewage pulp sludge. This practice of using peat in potting soils and the like can be environmentally unsound and results in the loss of environmentally sensitive bog areas.
Composting is a common process used to recycle organic wastes. The composting process reduces the volume of organic material and stabilizes nutrients, particularly nitrogen. Composting curtails environmental pollution and reduces, often significantly, the amount of recyclable organic matter requiring another method of disposal, which often is to dump it into a landfill site. Composting can also be used to process materials which cannot easily be dumped into a landfill site, such as the liquid raw manures obtained from the intensive rearing of farm animals in barns. Further, composting can be applied to waste organic materials derived from certified organic agricultural procedures. During the composting process, carbon and nitrogen compounds in the organic wastes are transformed by successive microbial populations into more stable complex forms which chemically and biologically resemble humic substances.
The commercial viability of existing composting facilities is primarily based on the operator receiving a fee for accepting the organic material from waste generators. The emphasis in most of these waste management composting facilities is the composting of large volumes of material to reduce the amount of material. The retention time in the composting channels or windrows is minimized to allow the maximum flow through. Sometimes the compost is allowed to cure outside the composting system to complete the bio-stabilization process. Under some commercial systems, little effort is made to maximize the quality of the finished compost material.
This invention seeks to overcome the long term consequences of the use of peat based growing media by providing agronomically acceptable growing media which are based on what are essentially otherwise waste materials. In a more particular embodiment, this invention seeks to provide agronomic growing media which are acceptable for certified organic cultivation in the greenhouse environment, as well as in field and garden use.
The fertility, and consequently usefulness, of agronomic growing media involve a complex series of interactions between the medium and the plants being grown in it. These include media pH, the form of the available resident nutrients, temperature, moisture content, media atmosphere, and the microbial populations present. The incorporation of compost into plant growing media can influence all of these factors. However, the indiscriminate use of poor quality compost in plant growing media can be counter productive, and can result in production fertility problems.
The development of the composting process to minimize the volume of waste organic material going to landfill sites has resulted in substantial quantities of compost becoming available, in which the quality of the compost can be maximized, so that the compost provides as much benefit in the growing media as can reasonably be achieved.
This invention utilizes high quality compost from optimized standard composting processes. This invention requires the composting process to be completed under strictly controlled conditions to produce fully bio-stabilized compost of known values of nitrogen, phosphorous and potash. The composting process is also completed under conditions which minimize the loss of nutrients due to volatilization and leaching. The amount of nitrogen, phosphorous and potash in the compost can be influenced by the selective use of the raw organic matter to be composted.
Further, the compost can be derived from certifiably clean xe2x80x9corganicxe2x80x9d materials, and thus can provide plant growing media suitable for certified organically grown food crops.
Thus, in its broadest embodiment, this invention seeks to provide a process for preparing plant growing media consisting essentially of:
(i) screening a fully bio-stabilized compost material to provide a retained fraction of particles under about 1 cm diameter, and a rejected fraction of particles having a diameter in excess of about 1 cm;
(ii) screening the retained fraction from step (i) into three further fractions to provide a rejected fines fraction below 1 mm, a medium fraction of from 1 mm to 4 mm, and a coarse fraction of from 4 mm to 1 cm;
(iii) remixing metered amounts of the retained medium and coarse fractions from step (ii) with an agronomically acceptable amount of humified organic matter having a particle size of less that 1 mm, and a cation exchange capacity of from about 10 meq/100 g to about 400 meq/100 g; and
(iv) remixing metered amounts of the product produced in step (iii) with an agronomically acceptable amount of a suitable bulking agent, to provide plant growing media product suitable for agricultural use.
Complete bio-stabilization in itself is not a new process in the context of the composting process. This invention requires the use of compost prepared by a process in which the bio-stabilization process has been fully completed during the composting process. The retention time in the composting process, depending upon moisture, temperature, aeration and feedstock mixes, must be sufficient to allow for full bio-stabilization. In addition, all good manufacturing practices for making compost that minimize losses of nutrients due to volatilization and leaching must be followed. The water content of the feedstock material is also adjusted to ensure optimum bio-stabilization, so that the final compost product used to make this invention is a dry particulate material.
In the first step of the process of this invention, the fully bio-stabilized and nutrient rich compost is screened to provide a retained fraction and a reject fraction. The particles greater than 1 cm diameter are rejected and further processed.
In the second step of the process of this invention, the compost fraction retained in the first step is separated into specific particle size components. The retained compost fraction is screened and separated into three fractions, which are:
(a) xe2x80x9ccoarsexe2x80x9d particles between 4 mm and 1 cm diameter;
(b) xe2x80x9cmediumxe2x80x9d particles between 1 mm and 4 mm diameter; and
(c) xe2x80x9cfinexe2x80x9d particles below 1 mm diameter.
These three fractions are accumulated conveniently in separate metering hoppers. The third fraction of fine particles below 1 mm diameter is separated and used for other purposes.
In the third step of the process of this invention, metered amounts of the coarse and medium fractions are transferred to a mixer scale and remixed under controlled conditions. The weight ratio of coarse fraction to medium fraction may vary, depending on the desired characteristics of the plant growing media. Preferred ratios are 1:1 and 2:3 by weight of medium to coarse.
In the fourth step in the process of this invention an appropriate amount of humified organic matter is added to the coarse/medium mixture from the third step. The humified organic matter can be any suitable organic matter with a particle size less than about 1 mm, and which has a cation exchange capacity of from about 100 meq/100 g to about 400 meq/100 g. In this context, the cation exchange capacity is defined as the total amount of exchangeable cations that a soil can absorb in its natural state. Suitable sources of humified organic matter include compost, black earth and low grade charcoal. The humified organic matter can be added to the coarse/medium mixture at a rate of between about 10% and 60% by weight of the final mixture. xe2x80x9cBlack earthxe2x80x9d is a commercial soil product in which decomposition of the plant organic matter has reached a more advanced stage, so that part of the organic material has passed into the condition known as humus.
In the fifth step of the process of this invention, an appropriate quantity of bulking agent is then added to the medium/coarse compost mixture to form specialized plant growing media. The bulking agent can be chosen from a wide range of possible materials, depending in part on availability, cost, and the properties required in the final product. Typical bulking agents include but are not limited to shredded plastic, brick fragments, wood chips, rock wool, vermiculite, or any of the bulking agents presently used by the horticulture industry. Both the amount and type of bulking agent used are chosen to suit the crops or plants to be grown in the final product.
In the sixth step of the process of this invention, if desired, nutrients in the form of organic or chemical fertilizers can also be incorporated in metered amounts into the plant growing media. If the plant growing media are intended for certified organically grown crops, then all fertilizer used must meet the organic certification requirements. The amount of fertilizer added to the plant growing media will depend on the natural nutrients in the medium/corse compost and the level of nutrients desired in the finished plant growing media products. The addition of fertilizers at this stage can thus be used to adjust the N:P:K ratio of the compost material used to a desired N:P:K ratio in the final product.
Ammonium nitrate is a preferred source of nitrogen, although urea can also be used. Other nitrogen sources include ammonium sulphate and calcium nitrate. The preferred sources of potassium are potassium nitrate, potassium sulphate and potassium chloride. The preferred source of phosphorus is mono-ammonium phosphate. Additional sources of phosphate are ammonium ortho phosphate, simple super phosphate and triple superphosphate. The above sources of chemical fertilizer can also be readily sourced by using the pelleted enhanced organic fertilizer disclosed in patent application Ser. No. 09/692,835.
In another preferred embodiment of this invention, the pelleted pure organic fertilizer disclosed in patent application Ser. No. 09/692,834 can be added to the plant growing media to provide a source of nutrients and comply with xe2x80x9corganicxe2x80x9d standards for organically grown food. The pure organic fertilizer can be produced with various concentrations of N:P:K and used to adjust the nutrient levels in the final plant growth media.
The fertilizers are added to give a desired N:P:K ratio in the final product and are chosen to be suitable for the plants or crops to be grown. In general, the values in the N:P:K ratio will normally be in the range of 2-20:1-20:1-20, and thus include such commonly used ratios as 10:10:10, 5:10:10, 5:5:5, 10:2:2, 2:10:2, and 3:2:10. The source of nutrients will depend on the price of the nutrients, the desired levels of the guaranteed analysis of the nitrogen, phosphorus and potassium in the plant growing media and the agronomic requirements of the crops being grown.
The compost coarse/medium fractions, humified organic matter bulking agent, and nutrients, if necessary, are mixed until thoroughly homogenous. The plant growing media are then bagged for shipping.